More precisely, the present invention concerns a method and system comprising:                a server system connected to internet, having a first cartographic database and a first routing engine, adapted to calculate routes from starting points to destination points, taking into account traffic information,        a mobile device wirelessly connected to the server system, having geolocating means to determine a current location, having a second cartographic database and a second routing engine,        wherein said mobile device is adapted to determine a destination point, and to transmit a corresponding routing request to the remote server system,wherein the server system is adapted to:        calculate a primary route from the current location to said destination point, said primary route comprising a list of maneuvering points each maneuvering point comprising geo-coordinates and a maneuver to be performed.        
Such method and system are known from U.S. Pat. No. 6,812,888. However, it may happen that the first (offboard) cartographic database exhibits some differences with regard to the second (onboard) cartographic database and the calculated primary route entails guidance errors on the mobile device, in particular nearby the maneuver points.
Such a problem is not handled by the prior art and there is a need to further optimize said combinations of offboard and onboard navigation systems and methods.
Moreover, regarding the Estimated Time of Arrival (‘ETA’) calculated by such a combination of offboard and onboard navigation systems and methods, the precision and update of ETA in the prior art disclosures is insufficient.